The PlentyOfFish owner Markus discovered a recording of a phone conference with Battelle that reveals the Adsense revenue share percentages. You can here it here at minute 24:40 where they uncover the percentages.
The numbers ?
Battelle annouces a deal with google and says that google takes a 15% adserving fee and then pays out 51% of the remaining 85% leaving you with ~43% net payout.
//added: Looks like Markus pulled his post on it. Get the MP3 before its deleted.